An ambient light sensor (ALS) senses the brightness of ambient light. There are many applications for ambient light sensors. Some mobile devices such as cellular telephones and personal digital assistants (PDAs) use ambient light sensors to detect ambient light conditions and adjust the screen output (i.e., the brightness of the screen) based on the ambient light information. Controlling the screen output based on the ambient light conditions facilitates power savings and, hence, extended battery life because the mobile devices may decrease the screen output (i.e., dim the screen) when ambient light levels are relatively low.
Conventional ALS systems typically use a single, filtered photodiode. FIG. 1 depicts a schematic diagram of one embodiment of a conventional ambient light sensor system 10. The conventional ALS system 10 includes a light source 12, an illuminated object 14, a monochromatic light sensor 16, an analog-to-digital converter (ADC) 18, and a digital processor 20. Light from the light source 12 is incident on the illuminated object 14, and the reflected light from the illuminated object 14 is detected by the monochromatic light sensor 16. In general, the monochromatic light sensor 16 generates an electrical signal such as a voltage signal that is dependent on the intensity of the detected light. The monochromatic light sensor 16 then sends the generated electrical signal via an analog line 22 to the ADC 18, which converts the analog electrical signal to a corresponding digital signal. The ADC 18 then sends the corresponding digital signal to the digital processor 20 via a digital line 24. The digital processor 20 uses the digital signal to generate a signal representative of the ambient brightness 26.
Using a single photodiode results in a single input channel. Although a single input channel is sufficient to approximate ambient brightness, other information regarding the ambient lighting cannot be obtained. For example, conventional single-photodiode ALS systems cannot detect color, correlated color temperature, or light source type. This limits the usefulness of conventional ALS systems to only brightness compensation.